1. Field of the Invention
The present invention relates to an object or product (including a machine, and a manufacture) and a method or process (including a simple method and a production method). In particular, one embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a memory device and a method for driving the memory device.
2. Description of the Related Art
Memory devices can be classified into single-level cell (SLC) memory devices in which a 1-bit (single-bit, 2-state) signal is stored in one memory cell using a digital signal “0” or “1” and multi-level cell (MLC) memory devices in which multi-bit (3-or-more-state) signal is stored in one memory cell using a digital signal “0” or “1”.
The single-level cell and the multi-level cell each have their own advantages. For example, the single-level cell has advantages such as high signal reliability (i.e., extremely low probability of a difference between a write signal and a read signal) and high access speed, while the multi-level cell has an advantage of storing a larger amount of data in one memory cell.
In view of the above, a memory device which can function as a single-level cell memory device and/or a multi-level cell memory device depending on use is desired. As an example of such a memory device, there is a memory device having a structure disclosed in Patent Document 1 in which a single-level cell region (also referred to as a region including a plurality of single-level memory cells) and a multi-level cell region (also referred to as a region including a plurality of multi-level memory cells) are separately provided. However, in order that a memory device having a small number of memory cells can function as both a single-level cell memory device and a multi-level cell memory device, it is preferable that each memory cell can function as both a single-level cell and a multi-level cell.